Photographic tracing cloth



' NOV. 16, 1943. NADEAU ET AL 2,334,215

PHOTOGRAPHIC TRACI NG CLOTH Filed July 10, 1941 H5). PRIOR ART MuLs/o/v,

GELAT/N sue.

CELLULOSE N/TRATE.

GELAT/N AND CELLULOSE N/TRATE.

CLOTH.

/-/ AND CELLULOSE N/TQATE,

LLULOSE N/TRATE.

CELLULOSE ACETATE.

EMULSION.

LA 7'/N SUB. GELAT/N-A/YD C ELLUL 055 N/ TRA TE L7 2 Yg; APPROX lMA TELY.00/ /N.

ELAT/N AND CELLULOSE lY/TPATE LAYER APPROX/MATELY. 00/ NY.

TH/CK;

\"TCELLULOSE-ACETATE.

60/e E NooeOu C ar/ 5 Sm/zf;

[N VEN TORS A 'TORNE YS Patented Nov. 16, 1943- PHQTOGRAPHIC TRACING CLOTH Gale F. Nadeau and Carl F. Smith, Rochester, N. Y., assignors. to Eastman Kodak Company. Rochester, N. Y., a corporation of New Jersey Application July 10, 1941, Serial No. 401,768

12 Claims. (01. 95-8) This invention relates to a'material on which tracings and drawings may be reproduced pho- The method we use is to coat a sized cloth base I on both sides with a solution of gelatin and celtographically and more-particularly to a simplified method for producing said material.

Photographic tracing cloth consists of a sheet of sized tracing cloth which is waterproofed on both sides to prevent aqueous photographic solutions from attacking the sizing of the cloth, a photographic light sensitive layer being coated over one or both of the waterproofing layers. The waterproofing layers consist of a cellulosic material such as cellulose nitrate, which material does not properly adhere to a starch-sized cloth without the application of some intermediate subbing material. When the exposed sheet containing the drawing or tracing is treated in aqueous solutions, even when a subbing material is used, the waterproofing layers may come loose and permit the water to reach and swell the starch sizing of the cloth, thereby making the drawing or tracing useless, Another objection to tracing cloth which is made in this way is that after photographic processing and drying of the material, the waterproofing layer and its emulsion sometimes peel or strip from the cloth base.

Another method for forming sensitive tracing cloths has been disclosed in the prior U. S. Patent 2,117,814, granted May 17, 1938, to Nadeau et a1. That method consists in using a layer of a mixture of gelatin and a cellulose ester, as a subbing layer, to overcome the poor adhesion of cellulose esters, such as cellulose nitrate, to cloth; using cellulose nitrate or other cellulose esters for the waterproofing layer. The principal disadvantage of such a practice lies in the complicated nature of the material thus prepared.

We have found that a less complicated procedure is productive of a sensitive tracing cloth having superior qualities.

The principal object of the present invention is to provide a method for overcoming the difficulties of complicated manufacture by the prior art methods, and to provide a photographic tracing cloth having superior qualities.

The objects are accomplished by preparing a material having fewer layers than the prior art product, and relatively thick waterproofing layers of gelatin and a cellulose ester; on each side of a sized cloth base. The objects are accomplished in other ways described hereinafter.

Fig. 1 of the accompanying drawing is a sectional view of the material prepared according to the method of the prior art cited.

Fig. 2 is a sectional view of the material prepared in the manner of the present invention.

lulose ester of such consistency that a relatively thick coating is obtained. After curing the coated cloth, we apply an emulsion layer, adhesively joining it to one side of the waterproofed base by a subbing means. Thereafter, we apply a layer of gelatin or a cellulose ester such as cellulose acetate, to the other side of the base to control curl.

Our invention will now be described with particular reference to the accompanying drawing. In Fig. 2, i represents the calendered starchsized tracing cloth base on which have been coated layers 1, consisting of gelatin and cellulose nitrate, from a solution of the following composition:

to which 100% of the weight of gelatin of acetic acid has been added. From this solution coatings at least .00l in. thick may be coated on the cloth.

The cellulose nitrate used in the solution is preferably a highly alcohol soluble low vsicosity nitrate. A suitable composition would be one which had an ethyl alcohol solubility of 30-100%, a viscosity of 2 to 5 seconds by the dropping ball method" and a nitrogen content of 11 to 12%. This composition, however, is given merely as an example, nitrates of diflerent compositions being also suitable. The nitrogen content in particular, may be higher or lower than that of the example stated above.

The preferred proportion of gelatin to cellulose nitrate in the solution is 1 to 4; although a ratio of 1 to 3 gives fair results. A ratio of 1 to 2 gives very poor results. i

The concentration of the gelatin and cellulose nitrate in the solution is a very critical factor also. We have found that when the concentration of these materials is as low as 2.4%, layers I do not adequately waterproof the tracing cloth. A concentration of approximately 4% gives fairly satisfactory results and higher concentrations such as 5-7% and higher, impart superior qualities to the element, since layers of the required thickness may be coated from solutions of such concentrations.

One explanation for the superior qualities of a sensitive tracing cloth prepared according to our invention, lies in the thickness of the water-- proofing layers 1. It is absolutely necessary that the layers have a minimum thickness if the tracing cloth is to resist the swelling action of water.

We have ascertained that it is practically impossible to coat waterproofing layers of the required thickness when using solutions possessing solid contents (gelatin and cellulose nitrate) in the range of 23% by the conventional coating methods. Operating according to concentrations of the present invention, 4-7% and higher, we are able to coat layers of the order of thickness of .0005-.002 in. Layers of this range of thickness give adequate waterproofing to the tracing cloth. It should be noted, that, while coating thicknesses may be regulated somewhat by the speed of coating, nevertheless, it is practically impossible to get the required thickness without using the concentrations of the invention.

Another feature which cooperates with the concentration of solution to give a superior product-is the ratio of the gelatin to cellulose nitrate. The preferred ratios are not sufiicient, per se, to impart 'thequalities we desire, but in combinat on with the preferred solid concentration of the coating solutions, superior qualities are obtained.

The superior qualities" we refer to are undercompanying drawing. The product prepared in the manner of our invention, Fig. 2 has a more simple structure, and it has all the advantages the waterproofing layers 3 of the prior art element; are not present, and their function is now s rved by the relatively thick layers 1 of gelatin and cellulose nitrate.

Aside from the simplicity of -manufacture of the product'according to our method, we have found that our tracing'cloth possesses an unusually high degree of transparency which is an important feature to the user. This would appear to be surprising, in view of the fact that the overall thickness of the element shown in Fig. 2 would generally not be appreciably less, and may be thicker than an element prepared according to the prior'art. While we do not attempt to explain this phenomenon, other than to say that it may be attributed partially to our .preferred'ratios, the benefit which inures to the We have found that when the user is obvious. product of ourinventio'n is used in a continuous operating blue-print machine, due to the high transparency, roughly three prints may be made in the time formerly required to produce two.

After coating the base I with the waterproofing layers 1, we coat one of the layers witha subbing layer from a'solution of the following typical composition:

Per cent Gelatin 1.2 Acetic acid 1.0 Water h 10.0 Methanol 52.8 Acetone 35.0

Following this, an emulsion layer 5 of the desired sensitivity, is coated in a well known manner.

On the opposite side of the element we may, although this is not absolutely necessary, coat a layer 6 of gelatin, cellulose acetate or other celluthe curl tendency of the sensitive tracing cloth.

. so stood by comparison of Figs. 1 and 2 of the ac- Instead of cellulose nitrate we may use other cellulose esters in the waterproofing layers 1, e. g., hydrolyzed esters, such as, cellulose acetate (precipitation value, 70%). As in the case where we use cellulose nitrate, we use a sulliciently concentrated dope solution of these esters that a waterproofing layer of adequate thickness (of the order of .0005.002 in. or more) is obtained. The ratio of elatin to these cellulose esters is also regulated to obtain the desired adhesion of the waterproofing to the cloth, and to simultaneously impart the desired clarity and waterproofing characteristics.

The term precipitation value, asused herein, is defined as described in the patent above cited and refers to a means for classifying cellulose ester according to their. degree of hydrolysis.

It is to be understood that We are not limited to the exact type of sensitive tracing cloth and the sequence of layers described in the above specification. For example; the support may be any type of tracing cloth or tracing paper which has been sized with materials that swell or dissolve in water. Other materials may be used for the waterproofing layer and additional layers of 1 sized cloth base, a single waterproofing layer of gelatin and cellulose ester at least .0005 inch thick and containing at least 7 5 per cent cellulose ester, and a light sensitive layer over the waterproofing layer. I

2. A light sensitive tracing cloth comprising a sized cloth base, a single waterproofing layer of gelatin and cellulose ester at least .0005 inchthick and containingat least 75 per cent cellulose ester on both sides of the base. and a light sensi tive layer over one of, the waterproofing layers.

3. A light sensitive tracing cloth comprising a sized cloth base, a single waterproofing layer of gelatin and cellulose nitrate at least .0005 inch thick and containing at least 75 per cent cellulose nitrate on both sides of the base, and a light sensitive layer over one of' the waterproofing layers.

4. A light sensitive tracing cloth comprising a sized cloth base, asingle waterproofing layer of gelatin and cellulose nitrate at least .0005 inch thick andcontaining at least 75 per centv cellulose nitrate on both sides of the-base, a gelatin layer over oneofthe waterproofing layers, a lightsensitive layer over the gelatin layer, and a cellulose acetate layer over the other waterproofing layer,

5. A light sensitive tracing cloth comprising a sized cloth base, a single waterproofing layer of gelatin and cellulose nitrate .001 inch thick and containing at least 75 per cent cellulose nitrate on both sides of the base, a gelatin layer over one of the waterproofing layers, a li htsensitive layer over the gelatin layer, and a cellulose acetate layer over the other waterproofing layer.

6. A light sensitive tracing cloth comprising a sized cloth base, a single waterproofing layer of gelatin and cellulose nitrate .001 inch thick and containing per cent cellulose nitrate on both sides of the base, a gelatin layer over one of the waterproofing layers, a light sensitive layer over the gelatin layer, and a cellulose acetate layer over the other waterproofing layer.

7. A process of making a light sensitive tracin cloth which comprises coating a sized cloth with a single waterproofing layer of gelatin and a cellulose ester from a solution depositing a layer at least .0005 inch thick and containing at least '15 per cent cellulose ester, and applying a light sensitive layer over said waterproofing layer.

8. A process of making a light sensitive tracing cloth which comprises coating a sized cloth on both sides with a single waterproofing layer of gelatin and cellulose ester from a solution depositing layers at least .0005 inch thick containing at least '15 per cent cellulose ester, and applying a light-sensitive layer over one of said waterproofing layers.

9. A process of making a light sensitive tracing cloth which comprises coating -a sized cloth on both sides with a single waterproofing layer of gelatin and cellulose nitrate from a solution depositing layers at least .0005 inch thick containing a at, least 75 per cent ,cellulose nitrate, and applying a light sensitive layer over one of said waterproofing layers.

- ing cloth which comprises coating a sized cloth 10. A process of making a light sensitive tracmg cloth which comprises coating a sized cloth on both sides with a single waterproofing layer of gelatin and cellulose nitrate from a solution on both sides with a single waterproofing layer of gelatin and cellulose nitrate from a solution depositing layers .001 inch thick containing at least per cent cellulose nitrate, applying a gelatin layer over one of the waterproofing layers, applying a light sensitive layer over the gelatin layer, and applying a cellulose acetate layer over the waterproofing layer on the other side of the cloth.

12. A process of making a light sensitive tracing cloth which comprises coating a sized cloth on both sides with a single waterproofing layer of gelatin and cellulose nitrate from a solution depositing layers .001 inch thick containing per cent cellulose nitrate, applying a gelatin layer over one of the waterproofing layers, applying a light sensitive layer over the gelatin layer, and applying a cellulose acetate layer over the waterproofing layer on the other side of the cloth.

GALE F, NADEAU. CARL F. SMITH. 

